Anatomy of a wastewater plant energy audit

March 9, 2010
Learn how Upper Allen Township conducted an audit of motor run times on existing equipment at its wastewater facilities with data loggers.

In Pennsylvania, Upper Allen Township conducted an audit of motor run times on existing equipment at its wastewater facilities with data loggers manufactured by Massachusetts-based Onset Computer Corporation.

Studies estimate that potential exists to reduce energy use 15% to 30% at U.S. wastewater plants. The extent of savings depends upon the facility size, type, technology and regional operating conditions. Motor replacement might reduce energy use about 2%, while modifications in process control might cut consumption 30%, according to the Consortium for Energy Efficiency (CEE).

The aeration process, which uses fans and motors, consumes the most energy. Gaining maximum efficiency in the aeration process is particularly important because it is a peak load operation, meaning the plant consumes large amounts of power when electricity prices are highest. Reynolds Energy Services, Harrisburg, Pa., conducted a detailed audit of the Upper Allen facility with an eye toward installing improved aeration technology that reduces energy use and meets environmental permitting requirements.


Equipment does not always perform as efficiently as manufacturers estimate, so  auditors attached Onset HOBO U9 Motor On/Off data loggers on existing equipment at the treatment plant and pumping stations to “see how equipment is actually operating,” says Michael Conchilla, Reynolds project development manager.

The project focused on motor loads, particularly for the larger equipment — aerators and pumps at pumping stations. “We had a dozen different motors being logged. We were looking for runtime patterns and how many hours per day they’re being used. Many of the motors run on/off, on/off in small intervals. We wanted to see what those patterns are, what the collective hours are and extrapolate that out on an annual basis,” he says.

Reynolds left the data loggers on for about four weeks, monitoring the motor fields. “I got great results from tying the loggers to feeders in electrical cabinets rather than deploying them only on the motors. Some of the motor casings were too large to get a good field reading. I’ll probably do this more in the future,” Conchilla says.

After retrieving the data loggers, Reynolds downloaded the information, and graphed and analyzed the data using HOBOware software, which allows quick readout and plotting of information with export to spreadsheets.

“We needed to understand the run time patterns for each individual motor. If you can extrapolate that out for a year you know how many kilowatt-hours each motor is using,” Conchilla says. “The township collects amp readings on a regular basis. This is used to estimate electrical draw on the motors. We use this and the runtime data to estimate actual kilowatt-hour usage for each motor.”

Reynolds will use the information to help Upper Allen determine where upgrades to the system are necessary and where the expense can be avoided. After the new equipment is installed, the energy services company will continue to use data loggers to confirm results, a necessity since Reynolds is operating under an energy services performance contract.

Thanks to the data loggers, Upper Allen now can move forward with its efficiency improvements, assured that any guesswork has been removed. “You can’t argue with the data,” Conchilla says. “They tell you what’s going on 24 hours a day.”

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